As higher performance is required of semiconductor devices, studies are made to improve the characteristics of the MISFET. As means of improving the characteristics of the MISFET is known a technique of introducing lattice strain into silicon crystal to thereby improve the mobility of the carriers flowing in the crystal. Lattice strain is introduced into the silicon crystal of the channel region of the MISFET, whereby the mobility of the carriers flowing in the channel region is improved, and the drive performance of the MISFET can be improved.
As a method for introducing lattice strain into the channel region of the MISFET, the technique of forming a film for applying stress called a stressor film is formed, covering the top of the gate electrode. As the stressor film, silicon nitride-based insulating film, such as silicon nitride film, silicon oxynitride film, etc., are widely used. A stressor film having a suitable stress corresponding to a conductivity type, etc. of the MISFET is formed from the side surface to the top surface of the gate electrode, whereby a required lattice stress can be introduced into the channel region.
The following are examples of related: Japanese Laid-open Patent Publication No. 2006-344663 and Japanese Laid-open Patent Publication No. 2007-158322.
The inventors of the present application have found that often the MISFET has the effect of the stressor film impaired and has the On-state current decreased.